Comprehensive developmental data gathered during adolescence in two longitudinally-assessed samples (born in the decade 1920-1930) provide a unique opportunity to study prospectively the personality, biological- maturational, and cognitive antecedents of the numbers of children later produced by 126 subjects. Intensive adult followup assessments of these subjects, as late as age 50, are available so that the relationships with adult characteristics, even beyond the child-producing years, can be evaluated. In addition, the adolescent offspring of these subjects have also been studied extensively, thus permitting determination of the degree of cross-generational correspondence in family size preference, as well as a comparative examination of offspring-parent personality correlates of family size. Furthermore, since the spouses of the subjects were also evaluated in the followup studies, the contribution of spouse's personality to family size, separately and in interaction with the subject's characteristics, can be investigated. It is expected that by thus delineating these intrapsychic and interpersonal antecedents and correlates in these cohorts from an earlier cultural era, it will be possible to propose more general principles concerning the role of psychological factors in fertility, principles applicable to and predictive of behavior in our current population-conscious milieu.